Method of light dispersion and preferential scattering of certain wavelengths of light for light-emitting diodes and bulbs constructed therefrom

ABSTRACT

A light emitting diode (LED) bulb configured to scatter certain wavelengths of light. The LED bulb includes a base having threads, a bulb shell, at least one LED, and a plurality of particles disposed within the bulb shell. The plurality of particles has a first and second set of particles. The first set of particles is configured to scatter short wavelength components of light emitted from the at least one LED and has particles with an effective diameter that is a fraction of the dominant wavelength of the light emitted from the at least one LED. The second set of particles is configured to scatter light emitted from the at least one LED, and has particles with an effective diameter equal to or greater than the dominant wavelength of the light emitted from the at least one LED.

CROSS-REFERENCE TO RELATED APPLICATION

This application is a Continuation of U.S. patent application Ser. No. 12/299,088, with a filing date of Oct. 30, 2008, which is an application filed under 35 U.S.C. §371 and claims priority to International Application Serial No. PCT/US2007/010467, filed Apr. 27, 2007, which claims priority to U.S. Patent Provisional Application No. 60/797,118 filed May 2, 2006 which is incorporated herein by this reference in its entirety.

FIELD OF THE INVENTION

The present invention relates to light-emitting diodes (LEDs), and to replacement of bulbs used for lighting by LED bulbs. More particularly, it relates to the preferential scattering of certain wavelengths of light and dispersion of the light generated by the LEDs in order to permit the LEDs to more closely match the color of incandescent bulbs, or to the preferential scattering of certain wavelengths of light and dispersion of the light of the LEDs used in the replacement bulbs to match the light color and spatial pattern of the light of the bulb being replaced.

BACKGROUND OF THE INVENTION

An LED consists of a semi-conductor junction, which emits light due to a current flowing through the junction. At first sight, it would seem that LEDs should make an excellent replacement for the traditional tungsten filament incandescent bulb. At equal power, they give far more light output than do incandescent bulbs, or, what is the same thing, they use much less power for equal light; and their operational life is orders of magnitude larger, namely, 10-100 thousand hours vs. 1-2 thousand hours.

However, LEDs, and bulbs constructed from them, suffer from problems with color. “White” LEDs, which are typically used in bulbs, are today made from one of two processes. In the more common process, a blue-emitting LED is covered with a plastic cap, which, along with other possible optical properties, is coated with a phosphor that absorbs blue light and re-emits light at other wavelengths. A major research effort on the part of LED manufacturers is design of better phosphors, as phosphors presently known give rather poor color rendition. Additionally, these phosphors will saturate if over-driven with too much light, letting blue through and giving the characteristic blue color of over-driven white LEDs.

An additional problem with the phosphor process is that quantum efficiency of absorption and re-emission is less than unity, so that some of the light output of the LED is lost as heat, reducing the luminous efficacy of the LED, and increasing its thermal dissipation problems.

The other process for making a “white” LED today is the use of three (or more) LEDs, typically red, blue and green (RGB), which are placed in close enough proximity to each other to approximate a single source of any desired color. The problem with this process is that the different colors of LEDs age at different rates, so that the actual color produced varies with age. One additional method for getting a “white LED” is to use a colored cover over a blue or other colored LED, such as that made by JKL Lamps™. However, this involves significant loss of light.

LED bulbs have the same problems as do the LEDs they use, and further suffer from problems with the fact the LEDs are point sources. Attempts to do color adjustment by the bulb results in further light intensity loss.

Furthermore, an LED bulb ought to have its light output diffused, so that it has light coming out approximately uniformly over its surface, as does an incandescent bulb, to some level of approximation. In the past, LEDs have had diffusers added to their shells or bodies to spread out the light from the LED. Another method has been to roughen the surface of the LED package. Neither of these methods accomplishes uniform light distribution for an LED bulb, and may lower luminous efficiency. Methods of accomplishing approximate angular uniformity may also involve partially absorptive processes, further lowering luminous efficacy. Additionally, RGB (red, green, blue) systems may have trouble mixing their light together adequately at all angles.

This invention has the object of developing a means to create light from LEDs and LED bulbs that are closer to incandescent color than is presently available, with little or no loss in light intensity.

SUMMARY OF THE INVENTION

In one embodiment of the present invention, at least one shell that is normally used to hold a phosphor that converts the blue light from an LED die to “white” light contains particles of a size a fraction of the dominant wavelength of the LED light, which particles Rayleigh scatter the light, causing preferential scattering of the red. In another embodiment of the present invention, the at least one shell has both the phosphor and the Rayleigh scatterers.

A further object of this invention is developing a means to create light from LED bulbs that is closer to incandescent color than is available using presently available-methods, with little or no loss in light intensity. In one embodiment of the present invention, the bulb contains particles of a size a fraction of the dominant wavelength of the LED light, which particles Rayleigh scatter the light, causing preferential scattering of the red. In another embodiment of the present invention, only the at least one shell of the bulb has the Rayleigh scatterers.

A yet further object of this invention is developing a means to disperse light approximately evenly over the surface of an LED bulb, with little or no loss in light intensity. In one embodiment of the present invention, the bulb contains particles with size one to a few times larger than the dominant wavelength of the LED light, or wavelengths of multiple LEDs in a color-mixing system, which particles Mie scatter the light, causing dispersion of the light approximately evenly over the surface of the bulb. In another embodiment of the present invention, only the at least one shell of the bulb has the Mie scatterers.

In accordance with another embodiment, the method comprises emitting light from at least one LED; and dispersing the light from the at least one LED by distributing a plurality of particles having a size one to a few times larger than a dominant wavelength of the light from the at least one LED or wavelengths of multiple LEDs in a color-mixing system in at least one shell of the LED bulb.

In accordance with a further embodiment, a method for creating light in an LED bulb that is closer to incandescent color than is available using presently available methods, the method comprises: emitting light from at least one LED; and preferential scattering of the red light from the at least one LED by dispersing a plurality of particles having a size a fraction of a dominant wavelength of the light from the at least one LED or wavelengths of multiple LEDs in a color-mixing system in an outer shell of the LED bulb.

In accordance with another embodiment, a method for dispersing light in an LED bulb, the method comprises: emitting light from at least one LED; and scattering the light from the at least one LED by distributing a plurality of particles having a size one to a few times larger than a dominant wavelength of the light from the at least one LED or wavelengths of multiple LEDs in a color-mixing system in an LED bulb.

In accordance with a further embodiment, a method for preferentially scattering light in an LED bulb, the method comprises emitting light from at least one LED; and scattering the light from the at least one LED by distributing a plurality of particles having a size one to a few times larger than a dominant wavelength of the light from the at least one LED or wavelengths of multiple LEDs in a color-mixing system in an LED bulb.

In accordance with another embodiment, an LED comprises an LED die; a shell encapsulating or partially encapsulating the die and having a plurality of particles dispersed therein, and wherein the plurality of particles are such a size as to disperse and/or preferentially scatter the wavelength of the light emitted from the LED.

In accordance with a further embodiment, an LED bulb comprises a bulb having at least one shell having a plurality of particle dispersed therein or in the bulb; at least one LED inside or optically coupled to said bulb; and wherein said plurality of particles are of such a size as to disperse and/or preferentially scatter the wavelength of the light emitted from the at least one LED.

BRIEF DESCRIPTION OF THE DRAWINGS

The accompanying drawings are included to provide a further understanding of the invention, and are incorporated in and constitute a part of this specification. The drawings illustrate embodiments of the invention and, together with the description, serve to explain the principles of the invention. In the drawings,

FIG. 1 is a cross-sectional view of light emitted from an LED having Rayleigh scattering from sub-wavelength particles.

FIG. 2 is a cross-sectional view of light emitted from an LED having Mie scattering from supra-wavelength particles.

FIG. 3 is a cross-sectional view of an LED bulb showing an LED embedded in a bulb, and the bulb and its shell containing both Rayleigh and Mie scatterers.

FIG. 4 is a cross-sectional view of an LED showing an LED die embedded in plastic, and the plastic and its shell containing both Rayleigh and Mie scatterers.

DETAILED DESCRIPTION

Reference will now be made in detail to the present preferred embodiments of the invention, examples of which are illustrated in the accompanying drawings. Wherever possible, the same reference numbers are used in the drawings and the description to refer to the same or like parts. According to the design characteristics, a detailed description of each preferred embodiment is given below.

FIG. 1 shows a cross-sectional view of light emitted from an LED being Rayleigh scattered from sub-wavelength particles 20 in accordance with a first embodiment. As shown in FIG. 1, typically the incoming light 10 will include a plurality of wavelength components, including a wavelength 50 based on the light-emitting material used within the LED (not shown). For example, in a typical LED emission spectrum, the wavelength 50 emitted from the LED corresponding to the color blue will be approximately 430 nm. As shown in FIG. 1, the incoming light 10 impinges on a dispersed set or plurality of particles 20 with an effective diameter 60. The effective diameter 60 is preferably a fraction of the dominant wavelength 50, which creates the condition for Rayleigh scattering of the incoming light 10. For example, the dispersed set of particles 20 can be 80 nm alumina particles. It can be appreciated that other suitable particles having an effective diameter 60, which is a fraction of the wavelength 50 of the emitting light source or LED and creates Rayleigh scattering can be used. It can be appreciated that the particles need not be spherical, or even approximately spherical, and that other shapes can be used such as disk or rod-shaped particles. As shown in FIG. 1, the short wavelength components 30 are scattered by the particles 20, while the transmitted light 40 having long wavelength components are substantially unaffected. The transmitted light 40 is thus enhanced in the color red relative to the incoming light 10, without significantly affecting light intensity.

FIG. 2 shows a cross-sectional view of light emitted from an LED having Mie scattering from a plurality of supra-wavelength particles 70 and an equal scattering of each of the wavelengths 80 according to a further embodiment. Typically the incoming light 10 will include a plurality of wavelength components, including a wavelength 50 based on the light-emitting material used within the LED (not shown). For example, in a typical LED emission spectrum, the wavelength 50 emitted from the LED corresponding to the color blue will be approximately 430 nm. As shown in FIG. 2, the incoming light 10 impinges on a dispersed set or plurality of particles 70 having an effective diameter 90, wherein the effective diameter 90 is greater than a dominant wavelength 50 of light emitted from the LED. The effective diameter 90 of the dispersed particles 70 are preferably a size one to a few times larger than a dominant wavelength 50 of the light emitting source. For example, for an LED producing a blue light, the dispersed set of particles 70 can be alumina trihydrate having a diameter of approximately 1.1 microns. It can be appreciated that any suitable particles having an effective diameter 90, which is greater than the dominant wavelength 50 of the emitting light source or LED and creates Mie scattering can be used. It can be appreciated that the particles need not be spherical, or even approximately spherical, and that other shapes can be used such as disk or rod-shaped particles. This creates the condition for Mie scattering of the incoming light 10, wherein each of the incoming wavelengths 50 are scattered into an outgoing wavelength 80. The transmitted light or outgoing wavelengths 80 are thus dispersed in directions relative to the incoming light 10, without significantly affecting the light intensity.

FIG. 3 shows a cross-sectional view of a Rayleigh and Mie scattering system 100 having an LED bulb 10 with an LED 120 embedded in the bulb 110 in accordance with one embodiment. The bulb 100 comprises an LED 120 embedded in an inner portion 130 of the bulb 110 and having an outer surface or shell 140, and a base 150 having threads. The LED bulb 100 contains within it at least one LED 120, which is emitting light. As shown in FIG. 3, the inner portion 130 and the shell 140 of the bulb 110 containing a dispersed set of particles 20, 70, to produce scattering of the light produced from the LED 120 in accordance with both Rayleigh and Mie scattering. The light emitted from the LED 120 may contain several wavelengths, but is undesirably enhanced in the blue due to limitations in current LED technology. In order to preferentially scatter the light emitted from the LED 120, the bulb shell 140 and the body or inner portion 130 of the bulb 110 contain both dispersed set of particles 20, 70 having a wavelength corresponding to both Rayleigh scattering 20 and Mie scattering 70. In the case of a LED 120, which produces a blue light, the dispersed set of particles 20, 70 produces light, which is more like an incandescent than the light emitted from the LED 120, (i.e., does not appear to be as blue) as well as being more dispersed than the light emission angle from the LED 120 would otherwise permit. It can be appreciated that the bulb 110 can have more than one shell 140, and that one or more of the shells 140 or the inner portion 130 can contain dispersed particles 20, 70, which produce Rayleigh and/or Mie scattering.

FIG. 4 shows a cross-sectional view of an LED 200 showing the LED die 220 embedded in a plastic material 230 in accordance with another embodiment. The LED die 220 is embedded in a plastic material 230 or inner portion 232 and includes a shell 240. The plastic material 230 and the shell 240 each contain a plurality of dispersed particles 20, 70 therein. The plurality of dispersed particles 20, 70 each having an effective diameter to produce Rayleigh and Mie scattering of the light produced by the LED 200. As shown in FIG. 4, the LED 200 contains within it at least one LED die 220, which is emitting a source of light having a defined set of wavelengths. Typically, the LED die 200 and the corresponding source of light will contain many wavelengths, but is undesirably enhanced in the blue and ultraviolet due to limitations in current technology. The LED shell 240 typically is coated with a phosphor that converts some of the light to a lower frequency, making the light color closer to incandescent, but still undesirably enhanced in blue. In the LED 200, the shell 240 and the body of the LED 230 contain both dispersed particles 20, 70, each having an effective diameter 60, 90 to produce Rayleigh and Mie scatterering of the source of light. The result is that the light emitted from the LED 200 is both less blue and more incandescent than the light emitted from the LED die 220, as well as being more dispersed than the light emission angle from the LED die 220 would otherwise permit. The addition of the dispersed particles 20, 70, can be in addition to the phosphor and optics that may be normally added to the LED 200. 

1. A light emitting diode (LED) light bulb, comprising: a base; a bulb shell at least partially enclosing an inner portion of the LED bulb; at least one LED located in the inner portion of the LED bulb, the at least one LED configured to emit light at a dominant wavelength; and a plurality of particles disposed within the inner portion of the LED bulb, the plurality of particles configured to scatter light emitted from the at least one LED, wherein the plurality of particles comprises: a first set of particles having an effective diameter that is less than the dominant wavelength of the light emitted from the at least one LED; and a second set of particles intermixed with the first set of particles, wherein the particles of the second set comprise a different material than the particles of the first set and have an effective diameter equal to or greater than the dominant wavelength of the light emitted from the at least one LED.
 2. The LED bulb of claim 1, wherein the first set of particles is configured to scatter short wavelength components of the light emitted from the at least one LED by Rayleigh scattering.
 3. The LED bulb of claim 1, wherein the second set of particles is configured to scatter the light emitted from the at least one LED by Mie scattering.
 4. The LED bulb of claim 1, wherein the bulb shell has a thickness and at least a portion of the plurality of particles is dispersed within the thickness of the bulb shell.
 5. The LED bulb of claim 1, wherein the at least one LED is configured to emit light having a wavelength of about 430 nanometers.
 6. The LED bulb of claim wherein the first set of particles is alumina particles.
 7. The LED bulb of claim 1, wherein the second set of particles has particles with an effective diameter of about 1.1 microns.
 8. The LED bulb of claim 1, wherein the first set of particles has particles with an effective diameter of about 80 nanometers.
 9. The LED bulb of claim 1, wherein the plurality of particles includes particles with at least one of the shapes selected from the group consisting of spherical, approximately spherical, disk-shaped, and rod-shaped, or any combination thereof.
 10. The LED bulb of claim 1, wherein the second set of particles is alumina trihydrate particles.
 11. The LED bulb of claim 1, wherein the second set of particles includes particles with an effective diameter of about 1.1 microns.
 12. The LED bulb of claim 1, wherein the bulb shell contains a phosphor.
 13. The LED bulb of claim 1, further comprising optics configured to disperse the light emitted from the at least one LED.
 14. The LED bulb of claim 1, wherein the at least one LED is a blue LED.
 15. A method of making a light emitting diode (LED) bulb, comprising: disposing at least one LED within an inner portion of the LED bulb, wherein the inner portion of the LED bulb is at least partially enclosed by a bulb shell, and disposing, within the inner portion of the LED bulb, a plurality of particles configured to scatter light emitted from the at least one LED, wherein said plurality of particles comprises: a first set of particles having an effective diameter that is less than a dominant wavelength of the light emitted from the at least one LED; and a second set of particles intermixed with the first set of particles, wherein the particles of the second set comprise a different material than the particles of the first set and have an effective diameter equal to or greater than the dominant wavelength of the light emitted from the at least one LED.
 16. The method of making an LED bulb of claim 15, wherein the second set of particles is alumina trihydrate particles.
 17. The method of making an LED bulb of claim 15, wherein the second set of particles has particles with an effective diameter of about 1.1 microns.
 18. The method of making an LED bulb of claim 15, wherein the one or more LEDs are configured to emit light having a wavelength of about 430 nanometers.
 19. The method of making an LED bulb of claim 15, wherein the first set of particles is alumina particles.
 20. The method of making an LED bulb of claim 15, wherein the first set of particles has particles with an effective diameter of about 80 nanometers.
 21. The method of making an LED bulb of claim 15, wherein the bulb shell contains a phosphor. 